1. Field of the Invention
The present invention relates to a current supply for LEDs. Thereby, a transformer principle is put to use which generates a triangular a.c. current, which varies periodically around a d.c. current value, through the luminescent diodes. By means of this process it is provided that both the charging and also discharging current of an inductive reactance in the load circuit flows as diode current through the luminescent diodes.
2. Description of the Related Art
High-power light emitting semiconductor luminescent diodes (“Light-Emitting Diodes”, LEDs), briefly referred to as light diodes, have long since achieved their place in many fields in which there is need for optical display systems or illumination systems having low energy consumption, such as e.g. in traffic and signaling technologies. Through decisive technical innovations in the field of light emitting semiconductor components, with the aid of which there can today be obtained a higher light yield and an extension of the color spectrum over the entire wavelength range of visible light between 780 nm (violet) and 380 nm (dark red), optoelectronics is, in terms of lighting technology, embracing completely new markets.
For the attainment of a uniform illumination of surfaces, diffuser plates are employed as a rule. Due to the mains operation, above all in case of outdoor applications, light housings are usually necessary in order to protect the electronic components employed from the penetration of moisture.
In order to understand the central idea of the present invention, there will be briefly explained below the most important features of conventional processes and technologies according to the state of the art for the production of semiconductor luminescent diodes, above all the so-called “Chip-On-Board” (COB) Technology, which has greatly increased in significance in the last few years.
In “Chip-On-Board” (COB) Technology, the raw LED-chip is applied to the circuit board, with conductive adhesive, with the structure and the terminals upwards (“face up”). This procedure is called, in Anglo-American terminology, “die bonding”. After the curing of the adhesive there is effected in a further working step the connection of the chip terminals with the circuit board with the aid of a wire bonder, known from the production of integrated circuits. Thereby, the individual chip terminals and the circuit board are connected by a gold wire. Through the employment of special circuit board materials excellent heat conduction properties can be attained. From this there results a longer working life and a higher light yield per unit area. After application of a polymeric layer, the LED array is protected from mechanical damage due to shock or vibrations. Special circuit boards with reflector layers thereby serve for light bundling and increase of light intensities at smaller emission angles.
In comparison to conventional LED modules, through the employment of luminescent diodes which are applied to a circuit board as an LED array by means of COB technology, there can be produced efficient illumination units of high light yield, long working life, space-saving construction and a relatively slight cost outlay. Due to the light current values which can be attained, these modules are interesting not only as signalling or background illumination, but can be directly put to use as illumination means. LED arrays produced with COB technology having an emission angle of 180° permit a bright illumination of surfaces with a homogeneous light distribution, which is comparable with illumination by means of illumination equipment with fluorescent lamps operated at 40 to 50 mA. A further plus point is the 50% lesser current consumption in comparison with such illumination equipment.
Point light sources formed of high power luminescent diodes with COB technologies are ideally suited for small work and reading lights, as flexibly employable light sources in spot illumination, as central light source for orientation lights etc.
From DE 100 26 661 A1 there is known a universal compact LED illumination module which can be employed for indoor and outdoor lights in mains operation and without employment of further operating devices, such as e.g. mains transformers or specially dimensioned switch power unit parts. The light emitting semiconductor components provided as light sources are thereby controlled and supplied with current via a capacitor power unit part. In the preferred embodiment of this invention, the light emitting surfaces of the individual luminescent diodes emerge lens-like from the molding mass. As outer structural form for the LED illumination module disclosed herein there serves a molding mass (e.g. a casting resin) or a housing in which the electronic components are mounted protected from the penetration of moisture. The module can thereby be operated as a lamp or light directly from a current supply mains, can be positioned anywhere, and can be economically produced.
In the case of conventional capacitor power unit parts according to the state of the art (in contrast to the electronic solution in accordance with the invention) the effective value of the input alternating voltage can be selected to be variable (e.g. between 100 VAC and 277 VAC); even a supply of the mains part with d.c. voltage is possible.
Since, however, in the case of a capacitor mains power unit circuit the size of the capacitors employed increases strongly with increasing operating power, only low powers can be realized with such a mains power unit with acceptable structural size. Further, the performance of the electrolytic capacitors conventionally employed in the capacitor mains power units deteriorates with a number of operating hours. For the reasons mentioned above there is needed for the operation of high power LEDs (having an operating power of up to 4 W) the employment of alternative electronic solutions.